The Classless system again.
With the very notable exceptions of magic and resonance, there are no capabilities that are reserved solely to certain archetypes.
And you know what that is? That is half the Archetypes.
If you remove 1) Mystic Adepts, 2) Physical Adepts, 3) Mages, and 4) Technomancers:
You are left with 1) Faces, 2) Street Sams, 3) Deckers, and 4) Riggers.
Half the archetypes are not open to all. At best that makes Shadowrun a hybrid system, not classless.
Riggers are the mundanes that actually come closest to getting hallowed turf... you literally cannot perform their signature ability if you're not a rigger. Or a post-chargen technomancer.
And here is the twenty million nuyen question:
How many times has the signature ability had
any bearing on your games? Honestly.
In my case, I have been playing predominantly Riggers since the end of 2nd / beginning of 3rd - so about twenty years if you don't count the time surrounding 4th I didn't play any games.
Do you know how many times I, or any character for that matter, where required to make any vehicle tests that I didn't ask for (in my case)?
Two.
That is it. Every other vehicle test that was made by me I asked to make.
Is my experience typical? Holy hell, I hope not!
On the flip side, I am not a special unique snowflake either.
Just how much does this so-called signature ability come into play when the players do not coax it out of GMs?
I am guessing, and I will freely admit it is a guess, not very often at all. I would be surprised if it actually made an impact more than 10% of the time.